A solar pump system produces and supplies fresh water by driving a pump through an inverter using energy generated from a photovoltaic module. This solar pump system can supply water and electricity most effectively. The solar pump system may be used in a variety of applications such as supply of drinking water, agricultural water and seawater desalination in areas where a fresh water network infrastructure is insufficient.
In particular, the solar pump system is regarded as an optimal system that can solve power and water shortage in a remote area by supplying groundwater without receiving additional energy, in the remote area where the power supply is difficult. The Government of India has authorized installations of 50,000 solar pumps in 2014 for irrigation and drinking water supply and is expanding installations of the solar pumps up to now.
FIG. 1 shows a configuration of a conventional solar pump system.
The conventional solar pump system shown in FIG. 1 is configured to have a solar module 100, an inverter 200, and a controller 300.
One of important control methods of the solar pump system that generates power using solar light is a maximum power point tracking (MPPT)-based control method. A solar inverter may generate a maximum power via the MPPT-based control method which always tracks a maximum power generation point from a solar cell.
Among the conventional MPPT-based control methods, a hill climbing method is the most basic MPPT-based control method. The hill climbing method finds the maximum power point by changing a duty by a certain amount of a displacement. Although a controller based on the hill climbing method has a simple configuration, there is a problem that the maximum power point estimation is slow in a sudden change of a solar irradiation quantity.
Among the conventional MPPT-based control methods, a disturbance and observation method is the most common MPPT-based control method. This method operates at the maximum power point by measuring a change of the power according to an increase or decrease of a voltage. This disturbance and observation method has a problem that a control performance is deteriorated when a light amount is low.
Among the conventional MPPT-based control methods, an impedance matching method uses a fact that an output of an solar cell becomes maximum at a point where an impedance of a load becomes equal to an impedance of the solar cell. The impedance matching method is excellent in tracking performance, but is somewhat complicated and requires a large number of operations.
Thus, in a solar pump system such as FIG. 1 using the MPPT-based control method for various conventional solar pump systems, in order that a controller 300 controls a voltage applied to a water pump 400, the controller utilizes a DC link voltage and an output current of an inverting module 52 as information for generating a PWM output waveform of an inverter 200 and for detecting a low voltage/over-voltage. That is, a voltage sensor 210 provides the DC link voltage of the inverter 200 to the controller 300. A current sensor 220 provides the output current of the inverter 200 to the controller 300. Thus, the controller generate the PWM output waveform therefrom.
However, a sudden increase in the DC link voltage causes an over voltage problem. A sudden drop in the DC link voltage causes a low voltage problem. The water pump 400 cannot operate under the low voltage and over-voltage conditions. Thus, frequent stoppages or changes of the operation state of the water pump 400 may cause a failure of the water pump 400 as in case of frequent frequency changes, and, thus, a lot of energy loss may occur.
Further, since a PWM-based variable frequency output from the inverter 200 is detected instead of an input power to the inverter 200 in a conventional approach, an accuracy of calculation of the output power is lowered. Thus, there is a problem that a stress of the water pump 400 is increased due to pulsation of the output frequency.
Since the controller 300 detects the voltage and output current of each node of the inverter 200 and performs the MPPT-based control based on the detected voltage and current, the controller 300 must accurately detect the voltage and the current. Thus, the higher the required accuracy, the higher a price of the sensor placed in the system.